The FAA announced it is grounding all models of the Boeing 737 Max 8. It was responding to worldwide concern after two recent crashes. But here is that question. If there are concerns about the plane, why did the agency insist for days that the plane was safe? FAA Acting Administrator Daniel Elwell says there is a reason. The agency acted after learning new information about the Ethiopian Airlines flight that crashed this week.

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DANIEL ELWELL: We're resolute in our position that we would not take action until we had data to support taking action. That data coalesced today.

INSKEEP: NPR's David Schaper covers aviation and is with us once again this morning. David, good morning.

DAVID SCHAPER, BYLINE: Good morning, Steve.

INSKEEP: What was the new data that they gathered?

SCHAPER: Well, there is evidence collected at the ground at the site of the impact of the crash. And there's also newly enhanced satellite imagery of the Ethiopian Airlines flight track in the sky as well as an analysis of the aircraft's configuration just after it took off. And that's what really drove this decision to ground the planes in the U.S. from the FAA perspective. Here, again, is FAA administrator Dan Elwell talking on a conference call with reporters.

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ELWELL: Both new pieces of information were added fidelity, missing pieces that we did not have prior to today that outlined the track from Ethiopian Airlines' track to Lion Air closer than anything we had up until today.

SCHAPER: You know, the acting administrator is saying here that there's now evidence that the crashes of the Ethiopian Airlines flight on Sunday and the Lion Air flight in Indonesia in October were similar. But what's interesting is that many other countries didn't need that evidence and acted days ago out of what they said was an abundance of caution, which kind of begs the question, why didn't the U.S. act a little sooner in a more precautionary way?

And part of the reason may be that there was just so much public pressure that was building on the FAA and the Trump administration to do this because of this second crash of a new plane, a new Boeing 737 Max 8 plane, in less than five months. And that alone is extremely unusual.

INSKEEP: And, of course, we heard from aviation officials, former aviation officials, on this program in the last few days.

SCHAPER: Right.

INSKEEP: The FAA was very focused on wanting to act only when they had data, and abundance of caution was not enough for them. Now they are acting, though. How's the traveling public affected?

SCHAPER: Well, you know, a lot of people - there will be, you know, several hundred, maybe a few thousand people affected. But the overall impact should be somewhat minimal. There's about 70 of these planes that were flying in the U.S. They took about 225 flights a day. The airlines that use these planes are Southwest and American. They had the 737 Max 8. And United flew a longer version, the 737 Max 9.

And those airlines to a great extent will just be able to swap out those planes and rotate other aircraft in to fill those routes. A few flights may be canceled here and there in those - in some cases. And in those cases, the airlines will just rebook passengers without change fees. And if the scheduling doesn't work out on a rebooked flight, they're - they are offering some refunds.

INSKEEP: Let me circle back now to the investigation, David Schaper, because this is effectively an acknowledgement that something is going on with the 737 Max 8 that has not been solved. How do investigators go about figuring out what that is?

SCHAPER: One of the key pieces of evidence, or two key pieces of evidence, are the so-called black boxes - which are actually orange, as we've reported before - the flight data recorder and the cockpit voice recorder. Those are now in France in Paris to be analyzed by the transportation accident agency there. That'll tell investigators an awful lot about what the plane was doing, what alerts were going off, what actions the crew was trying to take.

And both those devices were pretty badly damaged in the crash. So it may take some time for them to extract that data and really find out what was happening with the plane. And there could be quite a few different causes, as there often are.

INSKEEP: David, thanks for the update.

SCHAPER: My pleasure, Steve.

INSKEEP: NPR's David Schaper.

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INSKEEP: For the first time, we have a bit of evidence suggesting that the special counsel's Russia investigation may be done.

GREENE: Yeah. NPR has learned that a key prosecutor, Andrew Weissmann, is leaving the office. He helped build the case against former Trump campaign chairman Paul Manafort. Manafort, we should say, was sentenced a second time yesterday to serve a total sentence of about seven and a half years in prison.

JOHNSON: It's the strongest sign yet the special counsel is done investigating. Andrew Weissmann, one of the most prominent members of the team, is leaving the special counsel unit. Two sources tell me he's going to teach and do some scholarship at New York University. And they say he wouldn't be leaving unless the Russia investigation was complete.

I'm hearing to expect more signs of wrapping up in the next two weeks maximum. And remember, Steve, the lead FBI agent assigned to the Mueller probe started a new job in Richmond, Va., this month. Other lawyers have been moving on too, but Weissmann was the most well-known. He's been attacked by conservative talk show hosts and called a killer by Steve Bannon, one of President Trump's former advisers.

INSKEEP: And now he's moving on. And you indicate that that doesn't mean we're going to hear the end of the investigation tomorrow, but maybe in the next couple of weeks. And we will see. All this comes after Manafort's sentencing, which - second sentencing, I guess we should say. How'd that go down?

JOHNSON: The judge in Washington has sentenced Paul Manafort to serve almost four years in prison. Add that to the punishment Manafort received in Virginia last week. That means he'll spend about seven and a half years behind bars total. The D.C. judge, Amy Jackson, was not buying Paul Manafort's remorse yesterday. She said he used other people's money to support his own extravagant lifestyle. Too many houses for one family to enjoy, too many suits for one man to wear, she said.

She also said that Paul Manafort had spent his whole life spinning. He treated the legal process the same way. Problem is, Judge Jackson said, courts is one - courts are one of the places where facts still matter. And she said, saying I'm sorry I got caught is not an effective plea for leniency.

INSKEEP: Yeah, but help me out here, Carrie. In spite of criticizing Manafort in all the ways you just described, didn't this judge, like the judge in the other sentencing, give Manafort a shorter sentence than might have been possible under the law?

JOHNSON: In the D.C. case, the total maximum sentence was 10 years. The judge was bound to take into account part of the sentence the Virginia judge had given based on complicated legal rules and sentencing guidelines. So she did give him a lot of extra time, she said, because Manafort had committed a new crime while he was already indicted in D.C. that he had allegedly attempted to tamper with witnesses in his case while the case was ongoing.

INSKEEP: So you're telling me that when you work through the various factors the judge had to consider, this actually is a fairly strict sentence.

JOHNSON: Former prosecutors who had been kind of outraged about the light sentence, relatively light sentence, in Virginia last week seem to have come down to the idea that seven and a half years total is a more normal sentence for somebody like Paul Manafort, who of course had never been convicted of a crime before this one.

INSKEEP: OK. And now we should just note before we go that New York prosecutors have issued their own indictment against Paul Manafort.

JOHNSON: Yes, state charges which would not - which would remain even if President Trump does decide to pardon Paul Manafort on the federal offenses. There is a big question about whether double jeopardy applies here, whether Manafort is being charged with the same offenses in the federal and the state system. That's going to be key to any defense he mounts in New York state.

INSKEEP: Carrie, thanks.

JOHNSON: My pleasure.

INSKEEP: NPR's Carrie Johnson. And we'll note again, Carrie is reporting that a key prosecutor is leaving the Mueller investigation, which is seen as a sign that the Russia investigation may be done.

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INSKEEP: Now let's turn to a religious minority that suffered under the Islamic State in Syria and elsewhere.

GREENE: Yeah. We're talking about the Yazidis, a religious minority that ISIS tried to exterminate. With ISIS in Syria nearly expunged, some of those captured but now freed Yazidis are making their way home to Iraq.

INSKEEP: NPR's Jane Arraf has been covering the story of the Yazidis for years. She met some of those people who've been freed and is on the line from Cairo. Hi there, Jane.

JANE ARRAF, BYLINE: Hi, Steve.

INSKEEP: Who'd you meet?

ARRAF: Well, I met women who had been bought and sold repeatedly, their husbands executed, separated from their children. I talked to relatives of girls who had been sold when they were 10 years old. So ISIS considered this ancient minority infidels, and that made it permissible to them to kill them and buy and sell them as sex slaves. And then there were the boys in the camp for displaced Yazidis in Iraq. I met Mazen (ph), who was 13. He had actually even forgotten the language the Yazidi speak, and we spoke in Arabic, the language of his captors.

INSKEEP: Because he'd been in custody for several years. Thirteen-year-old couldn't speak his native language anymore.

ARRAF: Five years. Some of them have forgotten his name. And it was - you know, for Mazen and others, it was really hard. There wasn't enough to eat. They were moved from place to place as the Caliphate shrunk. He saw other children killed in airstrikes. And, Steve, he was in a training camp with other Yazidi children. He talked a bit about what ISIS taught him.

MAZEN: (Speaking Arabic).

ARRAF: So there he's telling me that they taught him how to shoot a Kalashnikov, Russian assault rifles, and other what he called light weapons. He was being trained to kill Yazidis, his own people.

INSKEEP: Really disturbing to hear that word Kalashnikov spoken by such a young-sounding voice. What else have you learned about the Yazidis, Jane?

ARRAF: So if we recall back to 2014, when the Yazidis fled the massacre now acknowledged as a genocide in Sinjar in northern Iraq, the U.S. actually came into the war against ISIS in part to help save the Yazidis. So it's five years later, and there are still more than 2,500 of them missing. Now, everyone who comes back, like Mazen, raises the hope among the families that more will be found. But a lot of them won't be.

They've been killed in airstrikes in Mosul and Raqqa. They've been sold onward to other groups. There's a human trafficking ring for children in Turkey. And Yazidis understandably are distraught. They're holding protests, and they're calling on the U.S. and others to help. The U.N. this week is starting to exhume mass graves because thousands of them were killed as well.

INSKEEP: Is there any reason, Jane, to think that some of those 2,500 people might be alive somewhere in the world?

ARRAF: So I talked to one of the Yazidi smugglers. And the way a lot of these people have been brought back is they've been purchased, or they've been smuggled out. Now, lately, with Baghuz in Syria falling, they're trickling out. But there isn't much hope for more than a few hundred of them because a lot have been killed, and some don't know who they are anymore. A lot of them were taken as children.